1. Field of Invention
The invention relates to a method for improving bundle cohesiveness of a bundle of aramid yarn, to a method for knitting, sewing, or braiding said bundles of aramid yarn, and to knitted tubes comprising said bundles for automotive applications.
2. Description of Related Art
Aramid cords of spun yarns or stretch broken yarns are frequently used as reinforcing materials in rubber, thermoplastic materials or thermosets. The aramid cord consists of two or more twisted spun yarns or stretch broken yarns which are plied into a cord. The cord is used as such or after being processed on suitable equipment as a knitting, a braiding or a fabric. The processing of such aramid cords on machines, however, is problematic and often leads to breakages or repeated stops of the knitting, braiding, sewing machine, or weaving loom, which is used. Furthermore, during processing such aramid cords easily lose filaments and polymer parts easily fall out of the individual yarns and form deposits on and in machine parts. Particularly, the blocking of needles used for knitting or sewing leads to irregularities in the final form of the reinforcement. As a result of these irregularities the cord reinforcement fails in the matrix and the lifetime of the reinforcing material is reduced drastically.
Bundles of aramid fiber have been treated with various components. For instance, in JP 10-158939, a bundle of multifilament yarn, including aramid fibers, is treated with an oil to prevent fluffing during finishing processes. In JP 09-041274, a bundle of aramid fibers is treated with a water-soluble polyester to improve bundling power, but the materials are used for completely different application, i.e., reinforcing materials for cement materials.
When bundles of aramid yarn are used for knitting, braiding, and sewing, the known bundles have the above-mentioned disadvantages. Suitable aramid yarns (fibers) are not known for such purpose. The term “bundle of aramid yarn” includes a bundle of at least two individual yarns, particularly cords made of aramid yarns.
In U.S. Pat. No. 4,455,341, a multifilament yarn of an aromatic polyamide, in particular poly-p-phenylene terephthalamide, was provided with a water-soluble size. In addition to the size, the yarn may be provided with a non-ionic wax. The sized yarn is used as warp and weft yarn in the weaving industry. It was now found (see example 3) that the friction of the non-ionic wax treated yarn is still too high to make these yarns optimally suitable for use in cord knitting machines. Therefore, there is still a need in obtaining yarns with a low coefficient of friction and, at the same time, having good bundle cohesiveness.